In recent years, an apparatus for receiving an elastic wave generated from the inside of a subject by a probe and imaging the structure of the inside is being studied and developed. As one of applications, a photoacoustic diagnostic apparatus that irradiates the inside of a subject with a laser beam, receives a photoacoustic wave generated from the inside of the subject by an ultrasound probe, and displaying a tissue image of the inside of the subject is proposed (refer to, for example, NPL1). In an example of the photoacoustic diagnostic apparatus, a subject (breast) is compressed by plates and an ultrasound probe and irradiated with a pulse laser beam over the plate. A photoacoustic wave generated on the inside of the subject is received by the ultrasound probe, and a tissue image of the inside of the subject is reconstructed and displayed. A two-dimensional scanning mechanism capable of performing a two-dimensional scan by the probe and a pulse laser generator facing the probe to obtain a tissue image of the entire subject (breast) is provided, and a photoacoustic wave is measured in a plurality of measurement points.
An ultrasonic diagnosis apparatus having a mechanism of performing a mechanical scan by a probe and a method for controlling the same are known (refer to, for example, PTL1). In the ultrasonic diagnosis apparatus, the probe is provided with a position detector, a speed signal is generated from a position signal, and the difference between a target position and target speed is fed back to a drive signal of the probe.
In those diagnosis apparatuses, at the time of receiving a photoacoustic wave or ultrasound generated in the subject by the probe, when there is a space between the subject and the probe, the picture quality of a tissue image of the part deteriorates markedly for the following reason. The acoustic impedance of air in the space and that of the subject are largely different from each other, and the ultrasonic wave hardly passes through the space. To avoid the issue, a matching agent whose acoustic impedance is close to that of the subject is inserted between the probe and the subject so as not to have a space. To prevent a space from being created at the time of performing a mechanical scan by the probe, the probe, the subject, and the plates have to be sufficiently closely attached to each other so as not to have a space.